The present invention relates to an improved flange for connection between an axial compressor and high-pressure rotor disc unit in a gas turbine.
As is known, gas turbines are machines which consist of an axial compressor and a turbine with one or more stages, wherein these components are connected to each other by a rotary shaft and wherein a combustion chamber is provided between the compressor and the turbine.
The gas output from the combustion chamber, which has a high temperature and a high pressure, reaches through corresponding pipes the different stages of the turbine, which transforms the enthalpy of the gas into mechanical energy available to a user.
In turbines with two stages the gas is processed in the first stage of the turbine in temperature and pressure conditions which are very high and undergoes a first expansion there.
Then, in the second stage of the turbine it undergoes a second expansion in temperature and pressure conditions which are lower than those used in the preceding stage.
It is also known that in order to obtain the maximum performance from a specific gas turbine it is necessary for the temperature of the gas to be as high as possible.
However, the maximum temperature values which can be obtained in use of the turbine are limited by the resistance of the materials which are used at present.
It is also known that in gas turbines a flange exists for connection between the axial compressor and the high-pressure rotor disc unit of the turbine.
In particular, at present this connection flange is usually made of alloy steel for high temperatures, even when the connection is provided with high-pressure rotor disc units which are made of alloys based on nickel.
The reason for this procedure consists in the fact that the flange is advantageously produced integrally with the shaft of the axial compressor of the turbine.
A problem which is particularly significant in the present art is therefore that of guaranteeing an optimal connection between the axial compressor shaft and the high-pressure rotor disc unit, in all the conditions of functioning of the machine.
In fact it should be noted that the method of connection between the axial compressor shaft and the high-pressure rotor disc unit of the turbine represents a crucial aspect of the design of any turbine, taking into account the fact that the connection flange must withstand satisfactorily and reliably the stresses to which it is subjected without giving rise to breakages or other similar problems.
In fact it is known that this connection flange is a mechanical coupling element which must have firstly sufficient resilience, such as to permit maintenance of correct interference with the high-pressure rotor disc unit of the turbine to which it is connected, during the normal cycles of the machine; additionally at the same time the flange must be mechanically resistant, in order to guarantee the stability of the machine for the service life indicated in the specification.
Furthermore, nowadays, the trend is to obtain gas turbines with increasingly high performance levels.
This involves the fact of having to increase the speed of rotation and the compression ratios, as well as the combustion temperature.
There is consequently also an increase in the temperature of the gases which expand in the stages of the turbine.
This therefore gives rise to an increase in the stresses on the flange for connection between the axial compressor and the high-pressure rotor disc unit in the gas turbine, such that the flange becomes a particularly critical component, with increasingly great difficulty in guaranteeing a service life which is adequate and in accordance with requirements, in particular in relation to the phenomena of creep or viscous creepage.
At present these connection flanges are produced according to a frusto-conical shape, with very small thicknesses, such as always to guarantee good compatibility with the rotor disc units which are connected to them.
However when the speeds of rotation and temperatures become high, the present connection flanges are subjected to particularly difficult operating conditions, especially in some areas of concentration of stress which, more specifically, are those which are close to the central axis and those in the area of coupling between the conical part and the outer ring of the connection flange.
The object of the present invention is thus to eliminate the aforementioned disadvantages and in particular that of providing an improved flange for connection between the axial compressor and high-pressure rotor disc unit in a gas turbine, which makes it possible to reduce the concentrations of stress; this therefore makes it possible to increase the speed of rotation and the compression ratios of the machines or to increase the temperature of the fluid, or to determine an appropriate combination of the two aspects.
Another object of the present invention is to provide an improved flange for connection between an axial compressor and high-pressure rotor disc unit in a gas turbine, which permits easy fitting and removal of the flange according to requirements.
A further object of the present invention is to provide an improved flange for connection between an axial compressor and a high-pressure rotor disc unit in a gas turbine, which is also highly reliable.
Another object of the present invention is to obtain a service life which is far longer than that which can be achieved at present with the connection flanges used.
Another object of the present invention is to provide an improved flange for connection between an axial compressor and a high-pressure rotor disc unit in a gas turbine, which is particularly simple and functional, has relatively low costs, and can be produced according to conventional processing operations.
These objects and others according to the present invention are achieved by producing an improved flange for connection between an axial compressor and a high-pressure rotor disc unit in a gas turbine as described in the independent claim 1.
Further characteristics of the improved flange for connection between an axial compressor and a high-pressure rotor disc unit in a gas turbine are indicated in the subsequent dependent claims.
According to the invention it has also been possible to determine that the reduction in the maximum stress values in the areas of concentration of the forces gives rise to a substantial increase in the service life of the flange.
In addition, the connection flange according to the invention can still be made of alloy steel, like the flanges according to the known art, and thus it can also be produced integrally with the shaft of the axial compressor of the gas turbine.